Transmitting apparatus and method in mobile communications system

ABSTRACT

A transmitting apparatus in a mobile communications system is disclosed. The apparatus includes: a data modulating unit which maps a predetermined number of data sets to one or more reference signal points of a symbol constellation; an inverse Fourier transforming unit which inverse Fourier transforms a data-modulated signal, generating a time-domain signal; a peak suppressing unit which suppresses the time-domain signal such that a peak power decreases when the time-domain signal meets a predetermined condition; a Fourier transforming unit which Fourier transforms the peak-suppressed signal and generates a frequency-domain signal; and a modifying unit which modifies the frequency-domain signal, and provides the modified signal to the inverse Fourier transforming unit, wherein the modifying unit is arranged to move, when a peak-suppressed signal point in the symbol constellation does not belong to a predetermined surrounding area, the peak-suppressed signal point to a point within the surrounding area.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to the technical field of mobilecommunications, and particularly relates to transmitting apparatuses andmethods which transmit a signal using a multi-carrier scheme.

2. Description of the Related Art

In a multi-carrier modulation scheme, a symbol period can be increasedand a guard interval can be inserted, etc., to effectively reducemulti-path interference, which is especially problematic in widebandradio communications. An orthogonal frequency division multiplexing(OFDM) scheme is especially promising in future radio communicationssystems. However, in the multi-carrier modulation scheme such as an OFDMscheme, each of multiple sub-carriers is mapped to a modulated signalindependently. Therefore, a transmit signal in the time domain mayexhibit a high peak power. Therefore, a large transmission poweramplifier back off must be maintained. This ends up becoming aparticularly large problem at a mobile terminal, in which decreasedpower consumption becomes important. For decreasing a peak power, ormore specifically a peak-to-average power ratio (PAPR), a number ofmethods have been proposed in the past.

For example, a PTS (partial transmit sequence) method, an SLM (selectedmapping) method, and an interleaving, etc., provides for changing atransmission scheme (data modulation scheme, a bit pattern in thefrequency direction, a symbol interleave pattern, etc.), making the peakpower small. In these methods, how the transmission scheme is changedmust be reported from the transmitter to the receiver. Therefore, thereis a problem that a radio resource is, to a certain extent, consumed forthe reporting (signaling), which causes a corresponding decrease in datathroughput. This problem causes a reduction in advantages for the OFDMof realizing high frequency utilization efficiency and high-qualitytransmission even in a multi-path environment.

A method which does not require signaling of auxiliary controlinformation (side information) such as the transmission scheme includesa clipping and filtering scheme. This scheme suppresses amplitude of asignal component having a peak power in the time domain, and filters,using a time domain filter, an out-of-band distortion caused thereby.Suppressing the amplitude corresponds to distorting an original signal.In other words, it may also be said that the clipping and filteringscheme superimposes an intentionally interfering signal to an originalsignal such that the peak power decreases. This method, which directlydecreases the peak power, has a strong tendency to cause a signalwaveform to deviate from the original waveform, which is not preferablefrom a viewpoint of a received error rate of a signal.

Moreover, a tone reservation scheme divides sub-carriers into those fordata transmission and those dedicated to peak suppression, amplitudeand/or phase being set such that only the peak voltage is suppressed inthe latter. This method, which makes it possible to maintain thesub-carrier signal for the data transmission, is preferable from thepoint of view of a signal error rate. However, some sub-carriers whichare not to be used in data transmission have to be secured, so that acorresponding amount of decrease in the data throughput occurs.

Schemes devised in light of these problems as described above include anACE (Active Constellation Extension) scheme. The ACE scheme, which alsoassumes the clipping and filtering scheme, superimposes an intentionalinterference signal to the original signal. The ACE scheme is devisedsuch that a symbol receive error rate does not degrade.

FIG. 1 shows a symbol constellation of a transmit signal used in a QPSKscheme. As shown, one each of the respective reference signal points S₁,S₂, S₃, and S₄ is shown for each quadrant. Distorting a signal waveformsuch that a peak power decreases corresponds to remapping a signal pointbeing mapped in alignment with each reference signal point to a pointwhich is somewhat distant from the reference signal point. In this case,what allows any remapping is the above-described clipping and filteringscheme. In the ACE scheme, a remapping to an area with a wavy line arrowand an area which is shaded is allowed, but remapping to others isprohibited. For example, remapping, to T₁, a signal point which wasmapped to the reference signal point S₁ is allowed, but mapping the sameto T₂ is prohibited. For convenience of illustration, the shaded area isdrawn such that it represents a bounded square, but theoreticallycorresponds to an unbounded area. Remapping in such an area makes itpossible to distort a signal waveform (i.e., suppress the peak power)without impacting signal point symbol determination. This is because theresults of a hard decision on the signal point T₁ always reach thereference signal point S₁. The ACE scheme as described above isdisclosed in Non-patent document 1.

-   Non-patent document 1: B. S. Krongold and D. L. Jones, “PAR    Reduction in OFDM via Active Constellation Extension,” IEEE Trans.    on Broadcasting, Vol. 49, No. 3, pp. 258-268, September 2003.

SUMMARY OF THE INVENTION Problem(s) to be Solved by the Invention

Now, when the signal point S₁ in FIG. 1 is remapped to T₁, the signalpower for the symbol ends up increasing. The peak power may besuppressed, but the average signal power could end up increasing.Moreover, when the number of multiple modulation levels increase, thecapability to suppress the peak power decreases.

FIG. 2 shows a symbol constellation used in a 16 QAM scheme. In FIG. 2,as in FIG. 1, areas to which a signal point may be remapped are shown asan area with a wavy line arrow and a shaded area. As shown, with the 16QAM scheme, an outer reference signal point may be remapped to an areawith a wavy line arrow or a shaded area, but four reference signalpoints neighboring the origin cannot be remapped to another signalpoint. Therefore, the capability to suppress the peak power ends upbecoming weak. Such a trend becomes salient with an increase in thenumber of multiple modulation values. Moreover, an area which may beremapped, as shown, functions to increase the signal power, so that theaverage signal power could end up increasing even if the peak powercould be suppressed.

When channel encoding for error correcting is applied to a transmit bitsequence and a soft-decision decoding is performed at the receiver, inthe ACE scheme, a large deviation in a transmit signal point may cause alikelihood at a bit level at the receiver to be greatly different. Inthe soft-decision decoding process, signals of relatively the samedegree of likelihood leads to a better functioning of the errorcorrecting, so that it is not preferable for bit signals of extremelydifferent likelihoods to appear in the middle of the soft-decisiondecoding process. In other words, there is a problem that an offset of asignal point that is allowed in the ACE scheme does not necessarilycontribute to an increased accuracy from a point of view of thesoft-decision decoding process.

The problem to be solved by the present invention is to seek a decreasedpeak and average powers of multi-carrier signals.

Means for Solving the Problem

According to one embodiment of the present invention, a transmittingapparatus in a mobile communications system is provided. Thetransmitting apparatus includes:

a data modulating unit which maps a predetermined number of data sets toone or more reference signal points of a symbol constellation; aninverse Fourier transforming unit which inverse Fourier transforms adata-modulated signal, generating a time-domain signal; a peaksuppressing unit which suppresses the time-domain signal such that apeak power decreases when the time-domain signal meets a predeterminedcondition; a Fourier transforming unit which Fourier transforms thepeak-suppressed signal and generates a frequency-domain signal; and amodifying unit which modifies the frequency-domain signal, and providesthe modified signal to the inverse Fourier transforming unit, wherein,the modifying unit, is arranged to move, when a peak-suppressed signalpoint in the symbol constellation does not belong to a predeterminedsurrounding area which surrounds the respective reference signal points,the peak-suppressed signal point to a point within the surrounding area.

Advantage of the Invention

The present invention makes it possible to achieve decreased peak andaverage powers of multi-carrier signals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an area to which remapping is possiblein an ACE scheme for QPSK;

FIG. 2 is a diagram illustrating the area to which remapping is possiblein the ACE scheme for 16QAM;

FIG. 3 is a flowchart illustrating an exemplary operation according toone embodiment of the present invention;

FIG. 4 is a detailed flowchart for performing a modification process(S5) in FIG. 3;

FIG. 5 shows a surrounding area (in case of a QPSK scheme) which can beset up according to an embodiment of the present invention;

FIG. 6 shows a different surrounding area (in case of the QPSK scheme)which can be set up according to one embodiment of the presentinvention;

FIG. 7 shows a surrounding area (in case of a 16QAM scheme) which can beset up according to one embodiment of the present invention;

FIG. 8 shows a different surrounding area (in case of the 16QAM scheme)which can be set up according to one embodiment of the presentinvention;

FIG. 9 is a drawing showing how the signal point is move to within thesurrounding area;

FIG. 10 is a drawing showing how the signal point is moved to within thedifferent surrounding area; and

FIG. 11 is a functional block diagram of a transmitting apparatusaccording to one embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Description of Notations

111 mapping unit; 112, 114 switching units; 113 inverse Fouriertransforming unit; 115 radio unit; 116 determining unit; 117 peaksuppressing unit; 118 fast Fourier transforming unit; 119 modifying unit

BEST MODE OF CARRYING OUT THE INVENTION

In one embodiment of the present invention, when a peak-suppressedsignal point in s symbol constellation does not belong to apredetermined surrounding area which surrounds respective referencesignal points, the peak-suppressed signal point is moved to a pointwithin the surrounding area. Such a point movement is preferable notonly from a viewpoint of peak suppression, but also from a viewpoint oftransmission signal power saving. The surrounding area spreads not onlyin a direction specific to a reference signal point, but also in alldirections with the reference signal point as a center. Therefore, forany of the reference points, a peak suppression effect may be secured tosome extent, which greatly differs from a conventional ACE scheme. Thesurrounding area spreads within a limited range within which thereference signal point is located. If a soft decision decoding isperformed, likelihoods at the bit level becomes equivalent (no salientdifferent exists), thereby making it possible to perform ahighly-accurate soft-decision decoding.

The predetermined condition may be that a peak voltage of a time-domainsignal exceeds a predetermined value.

It may be arranged such that, when the peak-suppressed signal point inthe symbol constellation does not belong to the predeterminedsurrounding area which surrounds the respective reference signal points,the peak-suppressed signal point is moved to a reference signal pointwithin the surrounding area, or such that, when the peak-suppressedsignal point in the symbol constellation does not belong to thepredetermined surrounding area which surrounds the respective referencesignal points, the peak-suppressed signal point is moved to a point on aborder of the surrounding area. Therein, it may be arranged that one oforthogonal modulation components is equally maintained between thepeak-suppressed signal point and the point on the border. Alternatively,it may be arranged that the point on the border of the surrounding areais positioned on a straight line which links two points, one of whichpoints being before the peak suppression and the other being after thepeak suppression.

Each of the surrounding areas is arranged to be a circular area whichsurrounds a reference signal point corresponding to each, or a squarearea which surrounds the reference signal point corresponding to each.

In the modifying unit, a modification scheme may differ for a datasub-carrier and for a null sub-carrier. More specifically, for the datasub-carrier, the peak-suppressed signal point may be moved to the pointwithin the surrounding area when the peak-suppressed signal point in thesymbol constellation does not belong to the predetermined surroundingarea which surrounds each of the reference signal points. Then, for thenull sub-carrier, it may be arranged for the peak-suppressed signalpoint to be moved such that a peak-suppressed signal power takes a valuewhich is no more than a predetermined value.

The transmitting apparatus may be provided at a radio base station ofthe mobile communications system.

According to one embodiment of the present invention, a method for usein a transmitting apparatus in a mobile communications system isprovided. The method includes:

a data modulating step of mapping a predetermined number of data sets toa reference signal point within a symbol constellation; an inverseFourier transforming step of inverse Fourier transforming adata-modulated signal, generating a time-domain signal; a peaksuppressing step of suppressing the time-domain signal such that a peakpower decreases when the time-domain signal meets a predeterminedcondition; a Fourier transforming step of Fourier transforming thepeak-suppressed signal and generating a frequency-domain signal; and amodifying step of modifying the frequency-domain signal, and make themodified signal the data-modulated signal in the inverse Fouriertransforming step, wherein the modifying step is arranged to move, whena peak-suppressed signal point in the symbol constellation does notbelong to a predetermined surrounding area which surrounds therespective reference signal points, the peak-suppressed signal point toa point within the surrounding area.

The transmitting apparatus may be a radio base station which wirelesslycommunicates with a user apparatus. In this case, the method may be usedonly for transmission data for the user apparatus conducting a signaltransmission at a rate lower than a predetermined transmission rate.

Moreover, the transmitting apparatus may be a user apparatus whichwirelessly communicates with the radio base station.

While specific numerical value examples are used to facilitateunderstanding of the present invention, such numerical values are merelyexamples, so that any appropriate value may be used unless specifiedotherwise.

Embodiment 1

FIG. 3 is a flowchart illustrating an exemplary operation according toone embodiment of the present invention. In the present embodiment, anOFDM signal is provided. In step S1, data to be transmitted aremodulated using some data modulation schemes. Of sequences of data thatrepresent control data or user traffic data, a predetermined number ofdata sets are mapped to one reference signal point on a symbolconstellation. For example, for a QPSK scheme, two sets of data aremapped to any of four reference signal points (corresponding to S₁, S₂,S₃, and S₄ in FIG. 1). Data to be mapped are typically channel-encodeddata, but do not have to be channel encoded. When an AMC (adaptivemodulation and channel encoding) control is performed, a data modulationscheme, etc., is appropriately changed.

In step S2, the data modulated signal is inverse fast Fouriertransformed. In this way, a signal in the frequency domain istransformed to a time-domain signal.

In step S3, a peak voltage of the time-domain signal is suppressed. Inother words, an intentional interference signal is superimposed on thetime-domain signal such that a peak voltage is suppressed.

In step S4, a peak power suppressed signal is fast Fourier transformed,and a frequency-domain signal corresponding to a peak-power suppressedtime-domain signal is derived.

In step S5, a modifying process is performed on the frequency-domainsignal.

FIG. 4 is a detailed flowchart for performing a modification process.The modification process is performed on a signal point on eachsub-carrier. In step S1, it is determined first whether a sub-carrier tobe considered is a data sub-carrier or a null sub-carrier. The datasub-carrier is a sub-carrier within a bandwidth usable for datatransmission. The null sub-carrier is a sub-carrier outside thebandwidth usable for data transmission. (In this connection, asub-carrier secured in the above-mentioned tone reservation scheme isthe sub-carrier within the bandwidth usable for data transmission, andis different from the null sub-carrier.) If the sub-carrier is the nullsub-carrier, the process proceeds to step S2, and if it is the datasub-carrier the process proceeds to step S3.

In step S3, it is determined whether the peak-power suppressed signalpoint belongs to a predetermined surrounding area. In the presentembodiment, a certain surrounding area is set that surrounds respectivereference signal point within a symbol constellation.

FIG. 5 shows surrounding areas which can be set for a QPSK scheme. Theillustrated surrounding areas are set as circular areas with a radius Rthat surround the respective reference signal points S₁, S₂, S₃, and S₄.The diameter (2 times R) of a circle is set as a certain proper valuewhich is smaller than a distance between neighboring reference signalpoints.

FIG. 6 shows different surrounding areas which can be set for the QPSKscheme. The illustrated surrounding areas are set as areas of a square Rwith each side of 2 times R, which side surrounding the respectivereference signal points S₁, S₂, S₃, and S₄. The length (2 times R) ofone side is also set as a certain proper value which is less than thedistance between neighboring reference signal points.

FIG. 7 shows surrounding areas which can be set for a 16QAM scheme. Theillustrated surrounding areas are set as circular areas with a radius Rthat surround the respective reference signal points. The diameter (2times R) of a circle is set as a certain proper value which is less thana distance between neighboring reference signal points.

FIG. 8 shows different surrounding areas which can be set for a 16 QAMscheme. The illustrated surrounding areas are set as areas of a square Rwith each side of 2 times R, which one side surrounding the respectivereference signal points. The length (2 times R) of one side is also setas a certain proper value which is less than a distance betweenneighboring reference signal points.

In this way, in one embodiment of the present invention, a surroundingarea is set that surrounds the respective reference signal points, toeach of which a predetermined set of data is mapped, the respectivesurrounding areas having the same level of bounded areas regardless of adata modulation scheme. These matters largely differ from areas used forthe ACE scheme. The data modulation scheme is not limited to QPSK and16QAM, so that any multi-value modulation scheme may be used.

In step S3 in FIG. 4, it is determined whether the peak-power suppressedsignal point belongs to a predetermined surrounding area. The signalpoint before peak power suppression is associated with a referencesignal point within the surrounding area. As described above, when atime-domain signal is deformed (when the time-domain signal issuperimposed by an interference signal), signal points mapped toindividual sub-carriers may move to points which deviate from thereference signal point. In step S3, for a signal point being mapped to adata sub-carrier to be considered, it is determined whether thepeak-power suppressed signal point falls within the circular area inFIG. 5, for example. If falling therein, the process proceeds to stepS7, and for a signal point which is mapped to the sub-carrier, nomodification is applied, and the process proceeds to step S8. As aresult of a determination in step 3, if the peak power-suppressed signalpoint does not fall within a surrounding area corresponding to thesignal point, the process proceeds to step S5.

In step S5, the peak power suppressed signal point is modified(re-mapped) such that it is modified (re-mapped) within a surroundingarea related to the signal point.

FIG. 9 is a drawing showing how the signal point is transferred towithin the surrounding area. The surrounding area is an area within acircle with a radius R centered on a reference signal point S. Supposethat, with a set of data being mapped to a reference signal point S, thepeak power suppression moves the signal point to S′. In the presentembodiment, the surrounding area also includes a border.

As an example, the signal point S′ may be moved to a point T₁ on aborder that has an equal I component or a Q component. When the signalpoint S′ is moved to a different point, the effect of peak suppressionends up decreasing. From a point of view of maintaining as large peaksuppression as possible, it is preferable to move it to a point on theborder. When the signal point S′ is moved back to the reference signalpoint S, a peak suppression effect contributed by the sub-carrierbecomes zero. From a viewpoint of simplifying a point transformation, asin a case of the signal point T₁, it is preferable to make I componentor Q component the same as for the signal point S′. Alternatively, froma viewpoint of simplifying a point transformation while maintaining anamount of phase rotation when the signal point S is changed to S′ thesignal point is preferably moved to a point on a straight line whichpasses through signal points S and S′. From such a viewpoint, as for thesignal point T₂, the signal point is preferably moved to a point ofintersection between the straight line which links the signal points Sand S′ and a border for the surrounding area.

As shown, as a result of peal suppression, when the signal point ismoved from S to S″, it is in the surrounding area, so that a position ofthe signal point is not modified. This corresponds to a case such thatthe process proceeds from step S3 to step S7 in FIG. 4.

FIG. 10 is a drawing showing how the signal point is moved to within thedifferent surrounding area; In this case, the surrounding area forms asquare whose side surrounding the reference signal point S is 2 times R.Except for a point with a different border area shape. the pointtransformation which is similar to what has been described inconjunction with FIG. 9 may be performed.

In the step S5 in FIG. 4, the point transformation such as shown inFIGS. 9, 10, etc., is performed to modify a signal point mapped to asub-carrier to be considered. Thereafter, the process proceeds to stepS8.

When it is determined in step S1 that the sub-carrier to be consideredis the null sub-carrier, the process proceeds to step S2.

In step S2, a signal power associated with the null sub-carrier isdetermined. The null sub-carrier corresponds to an out-of-bandfrequency, so that it becomes an out-of-band radiation if such a signalpower exists. In step S2, it is determined whether such an out-of-bandradiation is within an allowable range. If it is not in the allowablerange, the process proceeds to step S4.

In step S4, a signal power which is associated with the null sub-carrierfalls within an allowable range. Ideally, it is preferable for theout-of-band radiation to be zero, so that it may be also be possible touniformly set such a signal power to be zero. Alternatively, theout-of-band radiation within the allowable range may be used to suppressa peak power even a little. After the signal power of the nullsub-carrier is modified, the process proceeds to step S8.

In step S2, in a case such that the signal power associated with thenull sub-carrier is within an allowable range (including a case suchthat it is zero), the process proceeds to step S6, where the nullsub-carrier is not modified, and then the process proceeds to step S8.

In step S8, it is determined whether necessary modifications have beenperformed for all of the sub-carriers. If there is any sub-carrierunconsidered, the process returns to step S1, where the above-describedprocess is performed. If the process is completed for all of thesub-carriers, step S5 (modification process) in FIG. 3 is completed, andthe process proceeds to step S6 in FIG. 3.

In step. S6 in FIG. 3, the modified signal is inverse fast Fouriertransformed and a time-domain signal is generated for the modifiedsignal.

In step S7, it is determined whether the time-domain signal meets apredetermined condition. The predetermined condition may be expressed,for example, as a PAPR not exceeding a predetermined value, anout-of-band signal level not exceeding a predetermined value, or a cubicmetric (a metric calculated based on a third power of an amplitude) notexceeding a predetermined value. At any rate, the predeterminedcondition is a condition for determining that a peak-suppressed signalis suitable for radio transmission. If the predetermined condition isnot met, the process returns to step S3, so that the above-describedprocess is repeated. If the predetermined condition is met, the processproceeds to step S8.

In step S8, the processed signal is appended a guard interval, forexample, and is converted to a signal for wirelessly communicating inOFDM, which signal is transmitted to complete the process.

FIG. 11 is a schematic functional block diagram of a transmittingapparatus according to an embodiment of the present invention. Thetransmitting apparatus may be provided at any apparatus which transmitsa signal using a multi-carrier modulation scheme represented by OFDM.Typically, the transmitting apparatus is provided at a radio basestation of a mobile communications system. FIG. 11 shows a mapping unit111, switches 112 and 114, an inverse fast Fourier transforming unit113, a radio unit 115, a determining unit 116, a peak suppressing unit117, a fast Fourier transforming unit 118, and a modifying unit 119.

The mapping unit 111 performs data modulation and maps a predeterminednumber of sets of data that represent user traffic data or control datato one signal point on a signal constellation. The data modulationscheme may be constantly maintained or may be changed as appropriate.

The switches 112 and 114 switches signal transmission paths in responseto a switching control signal from the determining unit 116, which isdescribed below.

The inverse fast Fourier transform (IFFT) unit 113 inverse fast Fouriertransforms a modified or unmodified data-modulated signal, transforminga frequency-domain signal to a time-domain signal.

The radio unit 115 appends a guard interval to the time-domain signalfrom the IFFT unit 113, and converts the same to a signal for wirelesstransmission. The guard interval may be provided as a cyclic prefix(CP).

The determining unit 116 determines whether the time-domain signal fromthe IFFT unit 113 meets a predetermined condition, and determines whatis in the switching control signal according to the determined result.The predetermined condition may be expressed, for example, as a PAPR notexceeding a predetermined value, an out-of-band signal level notexceeding a predetermined value, or a cubic metric not exceeding apredetermined value. At any rate, the predetermined condition is acondition for determining that a peak-suppressed signal is suitable forradio transmission. If the predetermined condition is not met, theswitch 112 and 114 are switched using a switching control signal suchthat a signal from the IFFT unit 113 is provided to the peak suppressingunit 117 and a signal from the modifying unit 119 is provided to theIFFT unit 113. If the predetermined condition is met, the switch 112 and114 are switched using the switching control signal such that a signalfrom the IFFT unit 113 is provided to the radio unit 115 and a signalfrom the mapping unit 111 is provided to the IFFT unit 113.

The peak suppressing unit 117 suppresses the time-domain signal suchthat a peak power is suppressed.

The fast Fourier transforming unit (FFT) unit 118 fast Fouriertransforms the peak-power suppressed time-domain signal, generating afrequency-domain signal.

The modifying unit 119 modifies a signal of the frequency domain. Themodifying method is a method as described in conjunction with step S5 inFIG. 3.

The method for suppressing a peak power and modifying a signal pointaccording to the present embodiment may be applied to any mobilecommunications system which transmits a signal in a multi-carriertransmission scheme represented by an OFDM scheme. In a case the presentembodiment is used for a radio base station when the OFDM scheme isadopted for downlink, the present method may be applied to all userapparatuses, or it may be applied on a limited basis to some userapparatuses. For example, it may be arranged such that the presentmethod is applied to a user using a data modulation scheme with a lowdata rate (more precisely, an MCS with a low data rate) and the presentmethod is not applied to a user using a data modulation scheme with ahigh data rate (more precisely, an MCS with a high data rate). Acombination of MCS (modulation and channel coding schemes) shows acombination of a data modulation scheme and a channel coding scheme (ora data size).

From a viewpoint of suppressing a peak power and saving a transmissionpower, it may be preferable to uniformly suppress power for all users.However, when the peak power is suppressed, a signal error rate may endup being increased. The method according to the present embodiment makesit more difficult to increase a signal error rate in comparison to aconventional method, but, even so, some signal error rate may occur. Thesignal error rate causes a more detrimental effect on a systemthroughput with a higher data transmission speed. For example, supposethat the signal error rate is 10% (in practice, it does not become ashigh. It is an exemplary numerical figure for brevity of explanation.)For example, for a user transmitting a signal at 500 kbps in QPSK, thesignal transmission speed degrades to approximately 450 kbps. However,for a user transmitting a signal at 10 Mbps in 64QAM, the signaltransmission speed becomes approximately 9 Mbps, or degrades by 1 Mbps.The effects of suppressing the peak power and modifying the signal pointare greater for a user conducting data transmissions at a higher speed.Thus, as in the above, it may be arranged to apply the method accordingto the present embodiment not to the high-speed user, and only to thelow-speed user. Even for the low-speed user, the data rate degradationmay occur, which does not have a major effect on a throughput of theoverall system. Moreover, the fact that it is low speed means that adata modulation scheme (MCS) which is less prone to error is used, sothat error tolerance is higher relative to the high-speed user. In thisway, a power resource of a base station may be saved while maintainingthe throughput of the overall system at a high level.

Moreover, in a case the present embodiment is used for a radio basestation when an OFDM scheme is adopted for uplink, the present methodmay be applied to all user apparatuses, or it may be applied on alimited basis to some user apparatuses. For example, it may be arrangedto apply the present method only to a user apparatus located near a celledge (with a severe transmission power restriction) that requires peaksuppression. Moreover, for the user apparatus located near the celledge, a data modulation scheme (MCS) which is less prone to error isused, so that error tolerance is high, making it possible to expect alarger peak suppression effect.

As described above, while the present invention is described withreference to specific embodiments, the respective embodiments are merelyexemplary, so that a skilled person will understand variations,modifications, alternatives, and replacements. While specific numericalvalue examples are used to facilitate understanding of the presentinvention, such numerical values are merely examples, so that anyappropriate value may be used unless specified otherwise. A breakdown ofembodiments or items is not essential to the present invention, so thatmatters described in two or more embodiments or items may be used incombination as needed, or matters described in a certain embodiment oritem may be applied to matters described in a different embodiment oritem as long as they do not contradict. For convenience of explanation,while the apparatuses according to the embodiments of the presentinvention are explained using functional block diagrams, suchapparatuses as described above may be implemented in hardware, software,or a combination thereof. The present invention is not limited to theabove embodiments, so that variations, modifications, alternatives, andreplacements are included in the present invention without departingfrom the spirit of the present invention.

The present international application claims priority based on JapanesePatent Application No. 2008-15495 filed on Jan. 25, 2008, the entirecontents of which are hereby incorporated by reference.

The invention claimed is:
 1. A transmitting apparatus in a mobilecommunications system, comprising: a data modulating circuit which mapsa predetermined number of data sets to one or more reference signalpoints of a symbol constellation; an inverse Fourier transformingcircuit which inverse Fourier transforms a data-modulated signal,generating a time-domain signal; a peak suppressing circuit whichsuppresses the time-domain signal such that a peak power decreases whenthe time-domain signal meets a predetermined condition; a Fouriertransforming circuit which Fourier transforms the peak-suppressed signaland generates a frequency-domain signal; a modifying circuit whichmodifies the frequency-domain signal, and provides the modified signalto the inverse Fourier transforming circuit, wherein, the modifyingcircuit, is arranged to move, when a peak-suppressed signal point in thesymbol constellation does not belong to a predetermined surrounding areawhich surrounds the respective reference signal points, thepeak-suppressed signal point to a point within the surrounding area,wherein for a data sub-carrier, the peak-suppressed signal point isarranged to be moved to the point within the surrounding area when thepeak-suppressed signal point in the symbol constellation does not belongto the predetermined surrounding area which surrounds each of thereference signal points, and for a null sub-carrier, the peak-suppressedsignal point is arranged to be moved such that a peak-suppressed signalpower takes a value which is no more than a predetermined value.
 2. Thetransmitting apparatus as claimed in claim 1, wherein the predeterminedcondition is that a peak voltage of the time-domain signal exceeds apredetermined value.
 3. The transmitting apparatus as claimed in claim1, wherein, when the peak-suppressed signal point in the symbolconstellation does not belong to the predetermined surrounding areawhich surrounds the respective reference signal points, thepeak-suppressed signal point is moved to a reference signal point withinthe surrounding area.
 4. The transmitting apparatus as claimed in claim1, wherein, when the peak-suppressed signal point in the symbolconstellation does not belong to the predetermined surrounding areawhich surrounds the respective reference signal points, thepeak-suppressed signal point is moved to a point on a border of thesurrounding area.
 5. The transmitting apparatus as claimed in claim 4,wherein one of orthogonal modulation components is arranged to beequally maintained between the peak-suppressed signal point and thepoint on the border.
 6. The transmitting apparatus as claimed in claim4, wherein the point on the border of the surrounding area is arrangedto be positioned on a straight line which links two points, one of whichpoints being before the peak suppression and the other being after thepeak suppression.
 7. The transmitting apparatus as claimed in claim 1,wherein each of the surrounding areas is arranged to be a circular areawhich surrounds a reference signal point corresponding to each.
 8. Thetransmitting apparatus as claimed in claim 1, wherein each of thesurrounding areas is arranged to be a square area which surrounds areference signal point corresponding to each.
 9. The transmittingapparatus as claimed in claim 1, wherein the transmitting apparatus isprovided at a radio base station of the mobile communications system.10. The transmitting apparatus as claimed in claim 1, wherein thetransmitting apparatus is provided at a user apparatus of the mobilecommunications system.
 11. A method for use in a transmitting apparatusin a mobile communications system, comprising: a data modulating step ofmapping a predetermined number of data sets to a reference signal pointwithin a symbol constellation; an inverse Fourier transforming step ofinverse Fourier transforming a data-modulated signal, generating atime-domain signal; a peak suppressing step of suppressing thetime-domain signal such that a peak power decreases when the time-domainsignal meets a predetermined condition; a Fourier transforming step ofFourier transforming the peak-suppressed signal and generating afrequency-domain signal; a modifying step of modifying thefrequency-domain signal, and make the modified signal the data-modulatedsignal in the inverse Fourier transforming step, wherein the modifyingstep is arranged to move, when a peak-suppressed signal point in thesymbol constellation does not belong to a predetermined surrounding areawhich surrounds the respective reference signal points, thepeak-suppressed signal point to a point within the surrounding area,wherein for a data sub-carrier, the peak-suppressed signal point isarranged to be moved to the point within the surrounding area when thepeak-suppressed signal point in the symbol constellation does not belongto the predetermined surrounding area which surrounds each of thereference signal points, and for a null sub-carrier, the peak-suppressedsignal point is arranged to be moved such that a peak-suppressed signalpower takes a value which is no more than a predetermined value.
 12. Themethod as claimed in claim 11, wherein the transmitting apparatus is aradio base station which wirelessly communicates with a user apparatus.13. The method as claimed in claim 12, wherein the method is used forthe user apparatus conducting a signal transmission at a rate lower thana predetermined transmission rate.
 14. The method as claimed in claim11, wherein the transmitting apparatus is a user apparatus whichwirelessly communicates with a radio base station.